Photogrammetry And Objective Evidence

Last year AccuPixel published a blog demonstrating how drone based photogrammetry was being used to create objective evidence on how mountain biking trails were eroding.

We have patiently waited for the vegetation to die back and this month we returned to the trails and put the drone up. It was a very frosty day. Battery level warning was set a little higher than normal.

Why was objective evidence considered important? The short answer is the landowner is very hostile to mountain biking and despite a remit to support recreation has raised very subjective concerns in an attempt to ban MTB. Objective evidence remains the best method to set policy…and counter subjective objections.

Two flights and 40mins later both trails were covered.

Post Flight Analysis

The survey points from the 2021 survey were applied and both models processed. The dense cloud, DEM and ortho photo were saved and imported into the Global Mapper project.

Global Mapper is one of those applications that just grows on you. Jose loves it and just about any GIS question can be answered using its rich toolkit.

The 2021 and 2022 versions of the DEMs and orthomosaics were loaded as separate layers.

Dense cloud analysis showing point density. The trails – the important bits – are shown as high density areas.

The area is covered in dense vegetation lining the routes. We didn’t really want to measure changes in the bracken growth and dieback (but we could if needed) so the first step was to create a median centreline along the trails.

Then using the Buffer tool areas around the trails were created. Mountain biking trails are narrow and in these two cases 1m and 0.5m were enough to make sure the scope of analysis covered just the areas where erosion might have occurred.

Slope analysis using the dense cloud as 3D source

With the specific areas of interest we then ran the analysis on each using Global Mapper’s Measure Volume Between Surfaces… tool.

Using the Measure Volume Between Surfaces…tool in Global Mapper

The good news? In both areas any erosion or trail wear was too small to record changes. We do not know the volume of traffic so true objectivity is challenging but both trails are in active use and ridden regularly.

With considerable confidence we can say mountain biking isn’t causing measurable harm or damage.

The second set of analysis was to look into the future and review how rainfall and runoff might accelerate. Do the trails act as drainage channels? Are there any changes to be made that will divert or slow any flow?

Global Mapper has a Watershed analysis tool that maps runoff and flow using open government LIDAR derived DEMS as as the basis:

Watershed analysis in Global Mapper.

The image shows the trails in red with the orthomosaics of each trail, plus the contour lines and results of Global Mapper’s Watershed analysis tool.

The terrain is typically sand and gravel making it exceptionally well drained with poor topsoil. This geological feature has kept it undeveloped and now a superb area for recreation irrespective of the weather. The flow channels as predicted by Global Mapper show the trails follow natural ridge lines and most of the water will flow away from the trail, limiting runoff as a potential accelerant for erosion.

Watercourses drain into a reservoir. Had erosion been a problem downstream impacts can be understood and predicted

Both the trails are close to watercourses that drain into a reservoir. Had erosion been an issue and concern then any silt runoff may be causing harm to water management or wildlife further downstream.

This kind of analysis really helps us predict risks and mitigate them. Instead of fixing problems after the occur the mountain biking community can start to think about preventative changes ahead of causing damage.


Objective evidence is priceless and this kind of data will help the mountain biking community monitor and mitigate risk of erosion and potential harm to what is quite a fragile and precious environment.

It also helps the landowner and politicians understand the actual as opposed to the perceived level of harm an otherwise highly beneficial sport is causing.

This is what Simon and Jose love about photogrammetry and analysis. Creating 3D shapes are all very good but their true value is how the knowledge is applied to make the world a better place.

If you would like to know more about Global Mapper and the analysis of photogrammetry data then please use the contact us page to get in touch.

2 thoughts on “Photogrammetry And Objective Evidence”

  1. Great article! Policies based on Evidence and collected data is the direction we need to be moving. Keep mountain biking accessible for the public while developing the best trails with consciousness and preventative actions to ensure nature remains balanced

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